This application claims the priority of Japanese Patent Application No. 106016/1992 filed Mar. 30, 1992, which is incorporated herein by reference.
Various methods for synthesizing diamond in vapor phase have been known. These methods are classified by the way how to dissolve and activate a material gas.
(1) Hot Filament CVD Method . . . activating a material gas by hot filament heated at a high temperature. PA1 (2) Microwave Plasma CVD Method . . . activating a material gas by microwave plasma. PA1 (3) DC plasma CVD Method . . . activating a material gas by DC hot plasma. PA1 (4) DC Arc Plasma CVD method . . . activating a material gas by DC are plasma. PA1 (5) Are Plasma Jet CVD Method . . . activating a material gas by are plasma jet utilizing DC plasma torch or RF plasma torch. PA1 (6) Burner Method . . . activating a material gas by oxygen acetylene flame. PA1 (a) Stopping applying voltage between the anode and the cathode of the torch acting as a cathode (a cathode-torch in short hereafter) for stopping discharge between the anode and the cathode of the cathode-torch, PA1 (b) Applying voltage by the same power supply which has been applied between the anode and the cathode of the cathode-torch, between the cathode of the cathode-torch and the anode of the anode-torch at the same time of step (a), PA1 (c) Stopping applying voltage between the anode and the cathode of the anode-torch for stopping the discharge between the anode and cathode of the anode-torch, PA1 (d) Producing a transferable, outer plasma jet between the cathode of the cathode-torch and the anode of the anode-torch, PA1 (a) Two plasma torches are disposed in a relation in which extensions of central axes of two torches meet at a point. An outer, transferable arc plasma is born between a cathode of a torch (cathode-torch) and an anode of another torch (anode-torch). A substrate body is placed at a point on extension of the central axial line of the cathode-torch. A diamond film will be grown on the substrate body. PA1 (b) A torch has a three-fold, coaxial structure of electrodes. A cathode bar is mounted at the center. Two coaxial anodes enclose the cathode. Inner cylindrical anode is called a first outer electrode. Outer cylindrical anode is called a second outer electrode. Otherwise, the inner anode is simply called an anode, and the outer anode is called an outer electrode. Gas passageways are formed between the cathode and the first outer electrode and between the first outer electrode and the second outer electrode. Gas can flow in the passageways from the bottom ends to the front ends. The three-fold electrodes effectively contribute to protecting the electrodes against heat during the external discharge in action. A transferable, outer discharge spans a cathode of a cathode-torch and an inner anode of a anode-torch (first outer electrode). In the cathode-torch, the cathode is protected by letting inert gas flow in the first space between the cathode and the first outer electrode. In the anode-torch, the first outer electrode anode) is protected by letting inert gas flow in the second space between the first outer electrode and the second outer electrode. Since inert gas contains no carbon, the electrodes are not contaminated by carbon deposition. It is preferable to let hydrogen gas flow in other gas passageways, i.e. the space between the first outer electrode and the second outer electrode of the cathode-torch. Hydrogen gas is unlikely to induce instability of discharge. Vapor-phase reaction of hydrogen gas would not bring about deposition on electrodes. Without such bad effects, hydrogen gas cools electrodes. PA1 (c) Carbon-containing gas will be sprayed to the plasma jet from a separated nozzle. PA1 (1) One cathode-torch and plural anode-nozzles yield transferable, outer plasma jets therebetween. (M=1, N.gtoreq.2) PA1 (2) Plural cathode-torches and the same number of anode-nozzles yield transferable, outer plasma jets therebetween. (M.gtoreq.2, N&gt;M) PA1 (3) Plural cathode-torches and plural anode-nozzles more than torches yield transferable plasma jets therebetween.(M.gtoreq.2, N&gt;M) PA1 (1) Parallel transference of anode-nozzles along their central axes in the direction of receding from the cathode-torch, PA1 (2) Parallel transference of the cathode-torch along its central axis in the direction of receding from the anode-nozzles, PA1 (3) Rotation of the anode-nozzles in the direction of making the extensions of the central axes recede from the cathode-torch, PA1 (4) Rotation of both the cathode-torch and the anode-nozzles in the directions of making the extensions of the central axes deviate from the initial confluence O. All modes will be effective to enhance the plasma formation area. In practice, some of four modes will be utilized at the same time. In the case of plural cathode-torches (M.gtoreq.2, N.gtoreq.2), besides modes (1) to (4), other modes are also available. PA1 (5) Parallel transference of the cathode-torches in the direction of receding together, PA1 (6) Rotating the cathode-torches in the direction of enlarging the associated plasma area. PA1 (1) Parallel transference of anode-nozzles along their center lines to the direction of receding from the cathode-torch, PA1 (2) Parallel transference of cathode-torches along their center lines to the direction of receding from the anode-nozzle. PA1 (3) Inclining anode-nozzles for letting the extensions of the center lines deviate from cathode-torches, PA1 (4) Rotating anode-nozzles with the extensions of center lines of anode-nozzles deviating from the cross point O. PA1 (a) Shape of nozzle parts of the cathode-torches, anode-nozzles and gas supplying nozzles, PA1 (b) Gas flux ejected from the cathode-torches, anode-nozzles and gas supplying nozzles, PA1 (c) Component of the gas for producing plasma, PA1 (d) Electric power for maintaining plasma, PA1 (e) Pressure for producing plasma jets, PA1 (f) Shape, position of outlet, and gas flux of a carbon-containing gas. PA1 (1) The method and apparatus for producing diamond of this invention allow us to make a large plasma jet area by producing inner untransferable plasma jets, converting them to outer transferable plasma jets and associating them in a united one. PA1 (2) Besides the static enlargement of plasma jet area, this invention further widens the plasma area by dynamical operations. The outer, transferable plasma jet is further enlarged by parallel transference or rotation of torches in the direction of receding each other or in the directions in which center lines of torches deviate from the initial crossing point. PA1 (3) If a carbon-containing gas flowed in passageways of plasma torches, electrodes of the torches would be contaminated by carbon deposition, which would unstabilize the discharge. Prior art have failed to solve the instability of discharge. This invention forbids a carbon-containing gas from flowing in passageways of the plasma torches. Only an inert gas or hydrogen gas or a mixture of an inert gas and hydrogen gas flows in the torches. Electrodes of the torches are fully immune from carbon contamination. The difficulty of instability of discharge is solved. A carbon-containing gas shall be spurted from other nozzles to the confluences of outer plasma jets. Freedom from carbon deposition allows torches to keep plasma jets stable for a long time. PA1 (5) Carbon-gas-supplying nozzles spurt a carbon-containing gas to the confluences of plasma Jets from one pair of anode-nozzle and cathode-torch. Since the section of the plasma jets is small at the confluences, the carbon-containing gas can uniformly attain to central portion of jets. The plasma gas contains uniformly-distributed carbon. The uniformly carbon-distributed plasma Jet enables us to synthesize a wide diamond film with a uniform property on a wide substrate body. PA1 (6) This invention features flexibility. The plasma jet area can unlimitedly be expanded by increasing the numbers of cathode-torches and anode-nozzles. PA1 (7) This invention allows a plasma jet method to form a wide, uniform diamond film on a wide substrate body without impairing the most conspicuous advantage of plasma jet method, i.e. rapid synthesis. This is the most important advantage of this invention. PA1 (8) Formation of an outer, transferable arc plasma requires cathode-members and anode-members. Aforementioned Japanese patent Application No. 3-225100 employed plasma torches both for cathode-members and anode-members. Too many plasma torches forced the apparatus to become too bulky. Heavy torches imposed heavy burden on the device for moving or rotating the torches. Too many power sources heightened the parts costs. Large size of the torches decreased the freedom of displacement or rotation. On the contrary, this invention simply employs a nozzle as an anode which is light in weight, easy to manufacture. Furthermore the conversion from a torch to a nozzle simplifies the structure of the anode-members and the moving or rotating devices therefor and widens the scope and freedom of displacement and rotation.
The inventors think that a favorable method for synthesizing diamond at high speed is the DC plasma jet method which utilizes DC plasma torches. This invention is an improvement of the DC plasma Jet method. Many proposals have been presented with regard to DC plasma jet methods. They have advantages and drawbacks in any way. Prior methods will be explained in short.